web

The Micro-Frontends future

Between the end of 2021 and the early weeks of 2022, I spent some time looking at where the micro-frontends journey is arrived so far.
I analysed the different challenges where teams are struggling with, the anti-patterns that causes coupling in the long term, and what are the recurrent patterns used for solving them.

We discovered that micro-frontends enabled teams to work independently and contribute to medium-large size applications, iteratively evolving our applications and reducing the blast radio of potential issues.

However, the analysis couldn’t stop on what we have achieved till now.

I had to look forward, a step into the future.

I have to understand what are the missing pieces of this fascinating puzzle and try to picture what would make this architecture approach even better.

In this post, I want to share a bunch of ideas and trends that might spark some interesting conversations in the micro-frontends community.
The topics covered are taking into account the client-side, server-side and edge-side implementations of this architecture.

Finally, I am going to share what will be my focus for 2022 to the micro-frontends ecosystem.

More upfront design

One of the main challenges for micro-frontend architectures is answering the question: how “micro” is a micro-frontend?
This is a question many organizations are facing, and in the reality, there isn’t only one answer, we need to understand the context, the organization structure and its size, and the communication flow between team.
After several engagements with multiple teams working on distributed architectures, I’ve seen many times “distributed components” more than a micro-frontends implementation.
With distributed components, the domain knowledge was shared across the container and the “micro-frontend” or even between the container and multiple “micro-frontends”.
We are still struggling to find the right boundaries and there is sometimes a lack of understanding of how we should interpret micro-frontends when we implement them.
I think this understanding is a necessary step towards better maturity, mastering the application business subdomains is not an easy task and requires a deep knowledge of the application we are building.

However, I think there is a potential solution for mitigate this challenge.

Investing more time upfront on the whiteboard revising with multiple parts of the organization how split our business domains without compromising the user experience is a must.
When we walk out from these meetings, we should be have enough ground covered to kick off the project with confidence and review our decisions on a regular cadence to make sure our initial assumptions are still valid for reaching our goals.
Remember that we cannot capture everything upfront, a business and an organization today is likely to change in 6 or 12 months so we should revisit our micro-frontends boundaries on a regular basis.

Also, never forget the link between organization structure and software architecture, it’s important to be aware of it and take it into account in our design decisions.

Micro-frontends communication

When we have multiple micro-frontends in the same view, at some point they need to communicate with each others.

In the mental model I created for designing micro-frontends, it’s encouraged to communicate between micro-frontends using a publish-subscribe pattern for enforcing the boundaries between micro-frontends, avoid or at least reduce the design-time coupling that leads to more autonomous teams.

For implementing technically this pattern there are several options such as Custom Events, an event emitter library, or even reactive streams.

An important requirement came up in the last few months that I didn’t put too much emphasis at the beginning, probably because I gave it for granted, but it’s definitely something to be aware of.
Like for event-driven architectures on the backend, having a clear schema for an event will help to avoid mistakes during the integration phase. Moreover, a schema provides a clear understanding of what’s going on inside a specific application also for tech people who are not working on the codebase directly.

I discovered in one of the many Slack channels I follow, this event-bus library that definitely helps achieve a more structured communication between loosely coupled elements (micro-frontends but not only): https://www.npmjs.com/package/@trutoo/event-bus

@trutoo/event-bus for your micro-frontends communication

Considering micro-frontends is a distributed architecture, there is the need to have a more formal API or events management.
API or events are the way how teams interact, not only in micro-frontends.
It’s essential to understand that these practices are not helping only a developer to avoid mistakes when an event is sent but also facilitate the discussion between teams and provide clarity of intent.
I hope in the future there will be even more effort in simplifying the developer’s experience when we have large applications that are massively using loosely coupled communications strategies.
How nice would be having an event registry to consult every time we are developing new interactions between micro-frontends?

Finally, if you didn’t have a chance to see what PayPal is doing on micro-frontends communication, I highly encourage you to watch this great video!

https://lucamezzalira.wordpress.com/media/8ab1607c97e5b8f5865c7a8b340318faPayPal presentation during the Micro-Frontends Conference organized by hasgeek

Server-side rendering (SSR)

Server-side rendering architectures are the ones who are innovating more in the past few months, think about Next.js or the investment made by the team behind React 18 with server components.
We have some interesting solutions also on micro-frontends like module federation for Next.js, Piral, TailorX, ILC and many others.

For SSR micro-frontends applications there are quite a few topics we should start to look at more in depth.
These are the gaps I’ve individuated so far:

micro-frontends discovery: like the service discovery pattern for microservices but applied to the frontend. Using this pattern we could compose micro-frontends dynamically without any static reference to an endpoint in a system.
Imagine a micro-frontends infrastructure self-registering to a discovery service and a UI composer retrieving micro-frontends from the discovery service instead of being point-to-point with the micro-frontends itself 🤯
reference architectures on the cloud: there is a lack of guidance on how to build SSR micro-frontends architectures using popular cloud providers. This is a friction point that can be fixed relatively quickly and I want to help as much as I can.
leverage the serverless paradigm with micro-frontends: I believe serverless can provide a great speed of development delegating the infrastructure management to a cloud provider. At the same time, we have to shift our mindset in understanding which services we should leverage for specific workloads like micro-frontends.
For instance, I see the value to use a service like AWS Step Functions for simplifying the creation of micro-frontends considering it provides great integration with the entire AWS ecosystem. This allows us to embrace a low-code model that in the long run will simplify the maintenance.
This is one of the many patterns we can use on the cloud, but exploring these patterns with micro-frontends can be extremely fascinating (at least for me 😅).
A framework-agnostic React server components approach: having a mechanism for atomically reloading a portion of a view using SSR when data changes on the backend and seamlessly integrating with client micro-frontends. This will allow a hybrid architecture mixing up CSR and SSR using the right approach for every micro-frontend. Probably we can create such a mechanism today, but having a sleek implementation like in React 18 would be the final goal.

As you can see there are many opportunities in front of us, some more tangible like the reference architecture one, some more longer-term like the agnostic React server components approach.
Of this list, my focus will be on covering the reference architecture as well as the investigation of using the serverless paradigm for micro-frontends. I’ve already started working on the prototype for the reference architecture and I have some interesting prototypes on the serverless side as well. Stay tuned for further updates 😉

Partial hydration

Performance is key for every frontend application, including micro-frontends ones.
It’s been a while since I heard about the concept of “islands architecture”, however, I believe in the end this architecture might fall under the micro-frontends umbrella due to its principles and characteristics.
The interesting technique that islands architecture introduces is the possibility to enhance the performance of our server-side rendering applications by leveraging partial hydration.

In a nutshell, instead of hydrating the entire page, only the “islands” visible to the users will be hydrated immediately and the others will be hydrated if/when the user will visualise them.

Partial hydration is not a new technique, it’s available since 2019 (if I remember well), but I didn’t see any reference to this technique in micro-frontends applications. Considering the nature of micro-frontends and how partial hydration works I believe this technique should gain more popularity for optimizing further our SSR micro-frontend applications.

In this post, Addy Osmani provides useful resources for understanding better the concept:

https://lucamezzalira.wordpress.com/media/05183d9218e2178a406d66ba817ac427Partial Hydration resources

Finally, if you are interested in this topic, I encourage you to have a read this post where there is a list of UI frameworks that might use partial hydration.
I’m currently experimenting with Preact in a micro-frontends proof of concept, hopefully, I’ll be able to share more insights soon.

Micro-frontends and edge computing

When we talk about micro-frontends at the edge, we often think about Edge-Side Includes (ESI) markup language.
This time I am pointing to the compute capabilities that many CDNs are providing like AWS Lambda at the edge or Cloudflare workers.

The edge technologies are advancing fast and therefore part of applications can be moved towards the edge improving the latency and the scalability of our solutions.
However, in many web applications, we cannot consider only the computational effort to generate an HTML page using multiple micro-frontends but we need to account also the complexity of the entire application.

Computation is often the “easiest” problem to solve nowadays, less so when it comes to data gravity (database, multi-region data replication, writes vs reads with global infrastructure, data replication latency…), or authentication that usually is centralised and well secured in a specific region of your cloud infrastructure or even a data centre on-prem.

It’s true, SSR micro-frontends applications can benefit from edge computing but they require access to a multitude of other resources (data, authentication, caches…) that are not fully available on the edge yet.
We cannot really think to use the full power of the edge unless we have a workload very well encapsulated that doesn’t require any of these external dependencies.

I believe we will end up having a larger adoption of edge technologies in the future, but at the same time I think we have to understand better where edge technologies can be used with a real impact on our workloads and not just because is “cool” (hype-driven development anyone?) working with edge nodes.

In my opinion, edge computing will have great relevance for micro-frontends in the near future, especially for improving the applications’ performance, but it’s not as simple as it seems right now.

Deployment

In microservices, there are a set of consolidated practices for de-risking the deployment of new microservices versions like feature flags, blue-green deployment and canary releases.
In the past 12 months I didn’t see any effort for implementing similar practices with micro-frontends, a part from feature flags that look a well-known pattern for many teams.
I believe a deployment strategy that creates confidence in the development team is a must-have.
In a distributed system, where often continuous deployment is a reality, we have to create a safety net for developers who can iterate fast-moving their code from their laptop to a production environment without risking introducing bugs experienced by all the users in one go.
For SSR micro-frontends we can easily reuse existing tools and practices for releasing our infrastructure leveraging one of these mechanisms, although, those strategies are often not embraced for client-side rendering micro-frontends applications.

There are several ways we can implement them, client-side, server-side or even at the edge.
My recommendation is to implement one of these strategies as soon as possible because they can create a safer environment for your teams and the consequences might surprise you… in positive 😁

Routing

Strictly linked to the deployment strategy, client-side rendering micro-frontends applications are lacking a solid routing strategy.
All the implementations are using the same routing libraries we use to implement monolithic architectures.
Instead, I believe we can do better than this!

When we mix a routing library in conjunction with the deployment strategy described before, we can have a very smart routing that takes into account newer micro-frontends versions, different environments, or even different user roles.
We can also have tools that gradually increase the traffic towards versions and performs rollbacks in the same way.
For instance, when we develop containers or serverless workloads in AWS, we can easily set up the deployment strategy we prefer with a few lines of configuration:

Canary Release of an AWS Lambda Function using AWS SAM

The routing in the application shell can be orchestrated easily via an external JSON that provides the different possibilities available without the need of integrating this information into the application logic.
Finally, when this static JSON is combined with deployment logic I believe the combination can bring a lot of value reducing the risk of new versions and allowing dynamic configurations based on any logic your business would like to implement.

The routing and deployment are definitely areas of interest for me. I’ll invest time during the next months to remove the undifferentiated heavy lifting and allow teams to better control their deployments and routing. I hope I’ll be able to share what I’m working on sooner rather than later because the working group is very excited about these two topics 🚀

Micro-frontends management

I didn’t explore (yet) this area, but I have a list of tools to try for understanding the PROs and CONs with micro-frontends.

My focus will be mainly on monorepo because I believe with poly-repo we don’t need extra tools for managing code like we have when there are multiple independent projects sitting in the same repository.
Currently, these tools caught my attention:

I believe all of them have some features that might help to structure a monorepo strategy improving the developers’ experience.

It’s a stretch goal for this year, not sure I’ll be able to invest enough time in reviewing every tool but I’ll definitely keep an eye on this space because I believe there are more unexplored opportunities to improve the developer experience even further.
Any suggestion on tools to try is more than welcome, especially if you can provide a brief review of them when you share your experience 😁

Summary

As you can see, there is still a lot of ground to cover in the micro-frontends ecosystem but we made great step forwards in the past years.
This for me it’s a super exciting opportunity to shape many areas of improvement for a “young” architecture that is raising success across enterprise organizations globally.
I’m sure there is more to discover, and I hope this fast adoption will bring new insights into what does and doesn’t work in distributed UIs architectures.
There are other topics on my radar like WebAssembly, better security on the client-side, streamlining even further the developers’ experience and more, but the topics listed in this post should provide food for thought for all the community to improve this novel way to scale our applications and organizations for the next few months.

Identifying micro-frontends in our applications

I’ve always spent a lot of time reading, attending conferences, researching different topics and those learnings really helped me shape my career, one of them is definitely Domain Driven Design (DDD).

Let’s take a step back first, why am I talking about DDD?

One thing that always puzzled me in this industry is the lack of learnings from different technology communities, for instance, we can find quite a lot food for thoughts when we examine the principles behind microservices more than focusing on the bare implementation.
On the backend side, there are often practices, methodologies, more in general ideas, that are totally applicable on the frontend too, but often we don’t think how to do it.
Often just taking a step back, understanding why someone implemented a pattern over another, allows us to open up a world of opportunities that we would never think about because “it’s not the standard way to do things”.
Contaminations from different industries or technologies allow us to see the world from a different perspective, creating new possibilities not explored enough (or at all sometimes), giving us the possibility to apply concepts and mental model to our day to day work.

DDD key concepts

Ok, now we can explain why DDD is mentioned in a post where I talk about micro-frontends.
DDD brings on the table some of the key concepts for defining a micro-frontends because it helps our organisation to align the business with the tech side, unifying de facto 2 main areas of our companies: product and tech.
DDD starts with the idea of identifying parts of our application that represents a subdomain of the final application.
Usually, an application is focused on a core domain, for instance, Netflix core domain is streaming movies anywhere at any time, considering the domain is usually a complex proposition, DDD suggests to split the domain into multiple subdomains allowing a company to understand how to structure the company as well as the project.
Some examples of subdomains could be the authentication, customer support inventory management and so on.

Subdomains are divided into 3 categories:

. Core Subdomains: those are the main reason why an application should exist, core subdomains should be treated as a premium citizen in our organizations because they are the ones that deliver values above anything else
. Supporting Subdomains: subdomains related to the core ones but not key differentiators, those subdomains could support the core subdomains but at the same time are not essential for delivering the real value to our users
. Generic Subdomains: those are needed subdomains used for completing the platform and often the companies decide to go with off the shelf software because not strictly related to their domain, for instance, authentication or payments management, more in general anything that is not related to our code business

Inside each subdomain, tech and product teams should identify a ubiquitous language, or rather a way where business meets tech using the same language for identifying functionalities, objects but more, in general, the domain model.

Think about it, how often we speak with a product owner that defines part of an application in a completely different way from the techies!

Ubiquitous language is not a static language, should evolve with the business and the applications running alongside it.
In this way, we would be able to define a domain-model similar to what we discuss day to day with the domain experts, constantly up-to-date.
Let’s take Netflix for instance, I think we are all familiar with this famous streaming platform, a subdomain of Netflix might be the catalogue, inside it we can identify multiple areas with specific functionalities, those could be directly connected to backend APIs related to a subset of the entire application.
In Netflix case, they are using Backend For Frontend pattern (BFF) nevertheless the principles remain the same.

In this screenshot, we can identify some components, those might be linked to some microservices like the personalisation service, the catalogue per country, the most popular contents and so on.
Despite the technical integration that could be via backend for frontend, GraphQL, Server Side Rendering and so on, the most important thing to understand is that those areas are all linked to the same subdomain.

Therefore those microservices, as well as the frontend, should be encapsulated in a unique subdomain with its own ubiquitous language.

Following just an example to understand what a subdomain should contain:

An example of subdomain based on the Netflix platform

This is a fundamental step for identifying how to “slice” our application, understanding that the frontend is part of the subdomain allows us to think holistically about our web application.
If we then extend the concept to the infrastructure too, we finally see all the components for developing a subdomain in the hands of a team that can own Frontend, Backend and Infrastructure end to end without too many external dependencies.

Up to now, DDD was applied to the backend layer but not very often to the frontend as well, extending these concepts to the frontend allow us to easily identify our micro-frontends.
I’d like to highlight another important concept, a subdomain cannot (and shouldn’t) be recognised as a component in a page, it’s true that in each UI we can find links or graphical elements related to different subdomains but at the same time we need to understand that they are not standalone identifying a subdomain and they need to have teams owning a subdomain end to end as we are going to see in the next few paragraphs.

Identifying a micro-frontends bounded context

Following the DDD principles, identifying a micro-frontend becomes quite trivial.
Usually, there are 2 main scenarios to deal with on a day to day based: greenfield projects, usually very exciting for any developer but also more complicated because we don’t have real information about our user base and how they would consume our content; legacy projects, where we have a tons of information (if we have diligently tracked our users behaviours using Google Analytics or similar tools) and therefore it’s easier to rationalise a logical identification of bounded context across the entire platform following our users’ behaviours

Having data to consult is one of the best situations we can aim for, understanding the users’ behaviours allow us to easily identify the subdomains of our applications.
Let’s assume we see a huge amount of traffic consulting the landing page, then 70% of those users are moving to the authentication journey (sign in, sign up, payment…), from here only 40% of the traffic subscribes to a service or use their credentials for accessing the service.

Users’ behaviours example in an application

Those are good indications about our users’ behaviours in our platform, DDD would suggest starting from the domain model of our application identifying the subdomains and their related bounded context and having behavioural data supports us on how to “slice” the frontend applications,

Users’ behaviours are invaluable for identifying our micro-frontends.

In the example discussed before, if we think about the technical implementation, allowing 100% of our users downloading only the code related to the landing page will allow them to have a faster experience because they won’t download the entire application immediately and the 30% of users who won’t move forward to the authentication area will have just enough code downloaded for understanding our service.
Obviously, mobile devices with slow connections can only benefit from this approach for multiple reasons: less KB to download, less memory used, less Javascript to parse and execute and a faster first interaction of the page.

Greenfield projects are a bit more complicated to manage, identifying micro-frontends upfront without knowing how our users interact with the platform could result in bad experiences but nevertheless, we have to find a way for structuring our micro-frontends architecture.
In this case, working closely with the product team or the subject experts could make a huge difference.
In my experience, any startup or medium-large organization have always a team or a person that has a clear idea of how the platform should behave, that knows inside out the core domain of an organization.
This person or team is key for understanding how the user should behave and therefore how to identify the domain model of our application as well as our micro-frontends.

It’s essential to understand that a subdomains evolves with the business, never assume that is immutable!

In DAZN we have decided to split our Single Page Application into multiple subdomains based on the data retrieved in the past years, ending up with 5 different micro-frontends with a few components developed by external teams and embedded as dependencies in one micro-frontend.
We identified the following micro-frontends:

. Landing page
. Authentication
. Catalogue
. Playback
. Sports data
. User account
. Help
. Chat

For instance, Playback and Sports Data are components living inside the catalogue micro-frontends, the complexity of those 2 subdomains lead us to assign a team dedicated to each of those subdomains.
Those components are published in an NPM private repository and are treated as an external dependency for the catalogue micro-frontend.
All the others are SPAs or single pages loaded by our client side orchestrator.

The power of local decisions

Working with subdomains allow us to assign a team to a specific area of our application, now stop for a moment and think how powerful could be this concept…
One of the key thing that I’ve always envy to startups is how fast they are capable to move and how quickly they take decisions on architecture, design or UX even.
When they need to take a decision, it’s a matter of minutes or hours but not weeks like in large organizations where we need to have a quorum of people agreeing on the solution.
If we think even further, a startup can react very quickly because they can take local decisions, in their case a local decision is a company decision, but if we extend this concept to medium-large organizations, dividing an application by subdomains allow us to have “multiple startups” inside an organization, therefore, empowering a team to take local decisions will allow to speed up the delivery, reduce the frustration and brings on the table interesting concepts like independent builds and deployments, less external dependencies, less frustration and more innovation.
The outcome of using DDD for identifying a ubiquitous language and subdomains would be creating a cross-functional team composed by frontend developers, backend developers, manual QAs and dev-in-test working closely to their product team/subject expert and being able to take a wide range of local decisions, from product decisions to infrastructure decisions, being responsible of the subdomain end to end.

Obviously, this team cannot (and shouldn’t!) be compared to a remote island where any decision is taken locally, these teams have to collaborate with the rest of the organization using services like architects, cloud experts and other functions inside the organization following the boundaries created by the heads of the technical department.

Organization example where each team represent a subdomain

In the past years, I read a lot about DDD and I found an interesting box inside Domain Driven Design Distilled book that caught my attention and I think is worth to share in this post to enforce the concepts explained in this paragraph:

Bounded Contexts, Teams, and Source Code Repositories

There should be one team assigned to work on one Bounded Context. There should also be a separate source code repository for each Bounded Context. It is possible that one team could work on multiple Bounded Contexts, but multiple teams should not work on a single Bounded Context. […]

It is especially important to be clear that one team works on a single Bounded Context. This completely eliminates the chances of any unwelcome surprises that arise when another team makes a change to your source code. Your team owns the source code and the database and defines the official interfaces through which your Bounded Context must be used. It’s a benefit of using DDD.

from Domain Driven Design Distilled — chapter 2

5 suggestions for dividing your frontend monolith

Last but not least, I think would be helpful having some takeaways of this post based on my experience and what I saw so far:

Gather data: if you have a legacy project you can use Google Analytics or similar services for understanding how your users are interacting with your application, you will find a clear idea how your user base is interacting with your application.
For greenfield projects, engage with your product team or customer, add GA or similar tools in your web application and via data validate the initial assumptions. Remember, bounded context and subdomains evolve with your business, are not defined once and set in stone!
Talk with the domain experts: invest time with your product team or the domain experts in your company, understand their point of view, their roadmap, how they think to evolve the project, those are vital information for identifying the micro-frontends
Review the teams organization: don’t fall in the trap of defining once the teams and don’t change them anymore, teams, like your business, should be fluid, if you see that following DDD there are some teams crossing multiple subdomains, make the bold decision reviewing the internal organization, the entire business will benefit from it!
A micro-frontend could be a single page or a SPA or SSR: as long you are following DDD for identifying your subdomains, a micro-frontend may end up to be represented by a single page like in the case of a landing page, or a more complex solution based on a Single Page Application architecture or a Server Side Rendering one.
Components risk being not representative of a subdomain because tightly linked to the container where they are nested, therefore the overlap of multiple contexts could cause more issues than benefits.
Invest the right amount of time at the beginning of your project: designing an architecture upfront is not the best way for starting a project, usually an architecture should work iteratively, therefore we should start designing “just enough” and slowly but steady we enhance the design based on additional information we found engaging with the product team, developers and users.
When you are identifying the different subdomains of your application invest enough time because this decision could impact how to structure the tech teams as well as how much communication overhead your company is going to spend due to dependencies between teams